1. Field of the Invention
The present invention relates to a cyclometalated transition metal complex and an organic light emitting device manufactured using the same, and more particularly, to a cyclometalated transition metal complex that can emit red light by triplet metal-to-ligand charge transfer (MLCT) and to an organic light emitting device manufactured to include an organic layer comprising the cyclometalated transition metal complex.
2. Description of the Related Art
Organic electroluminescent devices (organic EL devices) are self-emission display devices in which when a current is provided to a fluorescent or phosphor organic compound layer (hereinafter, referred to as organic layer), electrons and holes are combined together in the organic layer, thereby emitting light. Organic EL devices are lightweight, can be easily manufactured using few components, and have high image quality and wide viewing angles. In addition, they can realize a high degree of color purity and moving pictures, require low power consumption, and can operate at low voltages. Due to these advantages, they are suitable for use in portable electronics.
In a general structure of an organic EL device, an anode is formed on a substrate, and a hole transport layer, an emission layer, an electron transport layer, and a cathode are sequentially formed on the anode. The hole transport layer, the emission layer, and the electron transport layer are organic layers formed of organic compounds. An operational principle of an organic light emitting device having such a structure will now be described in detail. When a voltage is applied between the anode and the cathode, holes injected from the anode move to the emission layer through the hole transport layer, and electrons that are injected from the cathode move to the emission layer through the electron transport layer. In the emission layer, the electrons and holes recombine and thus excitons are generated and light having a wavelength corresponding to a band gap of a material is generated by radiative decay.
According to an emission mechanism, materials that are used to form an emission layer of an organic light emitting device are divided into fluorescent materials that use singlet excitons and phosphor materials that use triplet excitons. These fluorescent and phosphor materials themselves can be used to form an emission layer, or they can be doped on an appropriate host material to form an emission layer. As a result of electron excitation, singlet excitons and triplet excitons are formed in a host. At this time, a statistical generation ratio of singlet excitons to triplet excitons is 1:3.
When an organic light emitting device has an emission layer formed of a fluorescent material, triplet excitons that are generated in a host thereof are not used. On the other hand, when an organic light emitting device has an emission layer formed of a phosphor material, both singlet excitons and triplet excitons can be used such that internal quantum efficiency reaches 100% (Baldo, et al., Nature, Vol. 395, 151-154, 1998). Accordingly, an organic light emitting device that has an emission layer formed of a phosphor material shows much higher luminous efficiency than an organic light emitting device that has an emission layer formed of a fluorescent material.
When a heavy metal, such as Ir, Pt, Rh, or Pd, is introduced to an organic molecule, a triplet state and a singlet state are mixed together through spin-orbital coupling that occurs due to a heavy atom effect, thereby enabling transitions that is forbidden and effectively emitting a phosphor light even at room temperature.
Recently, a green light emitting material of which an internal quantum efficiency can reach 100% has been developed using a phosphor material.
Although transition metal complexes containing transition metals, such as Iridium or Platinum, are being developed as a highly efficient emission materials using phosphor materials, their luminous efficiencies are not suitable for highly efficient full-color displays or white light emission applications having low power consumption.
Red light emission for full-color displays can be realized if a luminous efficiency of about 3 Im/W is realized, but currently, the maximum luminous efficiency only reaches as low as 1 Im/W.
Accordingly, there is a need to develop a red light emitting material having improved light emission properties by overcoming such conventional technical limitations in the development of red light emitting materials.